1. Field of the Invention
The present invention relates to a lithographic apparatus and a device manufacturing method.
2. Related Art
A lithographic apparatus is a machine that applies a desired pattern onto a target portion of a substrate. The lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs), flat panel displays, and other devices involving fine structures. In a conventional lithographic apparatus, a patterning means, which is alternatively referred to as a mask or a reticle, can be used to generate a circuit pattern corresponding to an individual layer of the IC (or other device), and this pattern can be imaged onto a target portion (e.g., comprising part of one or several dies) on a substrate (e.g., a silicon wafer or glass plate) that has a layer of radiation-sensitive material (e.g., resist). Instead of a mask, the patterning means can comprise an array of individually controllable elements that generate the circuit pattern.
In general, a single substrate will contain a network of adjacent target portions that are successively exposed. Known lithographic apparatus include steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion in one go, and scanners, in which each target portion is irradiated by scanning the pattern through the beam in a given direction (the “scanning” direction), while synchronously scanning the substrate parallel or anti-parallel to this direction.
Some lithography systems include scanners having one or more optical columns (e.g., light paths). Conventional scanners cannot expose a large area substrate in a single scan. One reason for this is that it is difficult to produce a single optical column capable of exposing a large target portion. For example, it would be desirable to be able to manufacture flat panel displays (FPD's) on panels with dimensions of the order of 2 meters along each panel edge, but it would be very difficult to produce a single optical column capable of exposing a target portion extending across substantially the whole width of such a pattern.
One way to address this problem has been to expose a full width of a panel using a series of separate optical columns arranged such that each optical column scans a respective track on the substrate. In this case, adjacent tracks abut, so as to expose the full width of the panel. Unfortunately, it is difficult to maintain separate optical columns in appropriate positions relative to each other to avoid a small gap arising between adjacent tracks or to avoid a small overlap between adjacent tracks. Such misalignments could affect the functionality of the device being manufactured, and in the case of FPD's, could result in the appearance of a highly visible line on the display.
Therefore, what is needed is a lithography system and method of using same that can be used to scan a large area substrate in a single scan.